The present invention relates to railway car underbody support structures. Railway cars, such as tank cars or hopper cars often utilize a pair of center stub sills for supporting the two end sections of the elongated railway car body. Each center stub sill is an elongated assembly carrying a railway car coupler assembly at the outboard end thereof and extending inboard underneath the longitudinal center line of the car to support the end of the car and to pass the longitudinal loads of draft and buff into the car body. The stub sill rides upon the center of a wheeled railway truck assembly which rolls upon the track. The stub sill carries laterally extending bolsters which support the sides of the car body, and during slight lateral tilting of the body the bolster bears upon upper side bearings located on each lateral side of the truck assembly.
The center stub sill structure is impacted by tremendous loads and passes these loads into the car body. Since the sill is connected to the body underside, large bending movements are produced at the point of outermost connection between the car body and the sill.
It has been the practice to construct the main center beam of the center sill assembly from generally Z-shaped beams welded along their abutted edge under the longitudinal center line of the car body. The bottom horizontal flange of the Z-shaped beams acted to laterally stiffen the unit while laterally outwardly extending bolster members were welded to these flanges. A more recent development in the art has been to fabricate the main center beam of the center sill from two upright side plates placed equidistant from the longitudinal center line of the car body. Separate horizontal flange members are usually welded to the bottom of the side plates and separate bolster members welded to the flange members.
Another construction has utilized a combination of the two constructions described above having an outboard end section of the main beam of the sill constructed of two Z-shaped beams and an inboard section of the main beam constructed of two side plates welded to the Z-shaped beams. This construction permits the use of a single bolster member which is welded to the underside of the side plates to support both sides of the car body above the side bearings.
Each of the prior art constructions described has the drawback of requiring a weld between separate pieces of metal plate at points which are subject to tremendous train loads and thus these weld lines present areas of potential weakness and cracking. Of course, cracking of the sill assembly may lead to shortened car life, increased maintenance and out-of-service costs, and possible failure of the assembly which may cause a derailment and personal injury. Also, the greater number of welds required to construct the sill structure, the greater the labor costs of fabrication.
The primary reason that prior art constructions have utilized a relatively large number of separate metal plate parts welded together is that it has been recognized that if a large irregularly shaped part was cut from a piece of stock metal plate an excessive amount of metal plate waste would be created, and it was therefore not economically feasible to cut such large unitary parts.
It is therefore the goal of the railway car design engineer, 1) to design the stub sill assembly to have the least number of separate parts requiring the least number of welds, 2) to locate the welds in areas of reduced load and bending movement and 3) to minimize the amount of scrap metal plate produced during cutting of the parts from stock metal plate. It is a further goal of the design engineer to produce the strongest car support structure with a minimum of material and labor costs, a minimum of material weight and improved fabrication methods to effect the goals enumerated above.